Revisions from previous version
The correct and final IAU names are listed for all craters.
I reconciled the database with other existing crater databases
and I list discrepancies.
I removed some of the entries that I thoght were either not
useful or too difficult to consistently categorize.
I updated the database to correct errors and to include craters
missed in previous version.
Entries in Main Database
Below I summarize measurements made on each crater in the
database. Parentheses indicate notation used in tables. In the
tables, blank entries indicate that not enough data was available
to make the measurement. An "x" as an entry indicates the
feature does not exist or cannot be measured. All distance and
location measurements were made with digital images at C1-MIDR
resolution (225 m/pixel). The minimum possible error of any
distance measurement is therefore 122.5 m. However, the choice
of endpoints for a particular measurement is subjective, and the
repeatability of this choice dictates the true error in a
measurement. To assess this I repeated the analysis several
times for a subsample of the database and then found the standard
deviation for each measurement type. If the error was constant
with increasing crater diameter then we give the absolute average
standard deviation below. However, some measurements had errors
that systematically increased with increasing crater diameter, so
that it is more appropriate to give the average percentage
deviation.
Reference number (#). For reference purposes, each crater is
assigned a diferent number.
Name. Official IAU name.
Latitude (Lat) of crater center. Error is ± 0.05°.
Longitude (Lon) of crater center. Error is ± 0.05°.
Rim-to-rim diameter (D). Value is diameter of a circle with an
area equivalent to the crater's. I measured the area digitally
by outlining the rim and counting the number of enclosed
pixels. For craters with terracing, the rim is defined by the
outermost boundary of the observable terraces. Most previous
studies on other planets were made with photographic products
rather than digital data, and typically involved measuring
diameter using a set of rim-to-rim measurements or by fitting
circle templates to the craters. In most cases the end result
is nearly the same. Error is ± 2%. For crater fields, the
equivalent single crater diameter (SD) entry of the multiple
impacts database is used for D.
Confidence level (Co) that structure is an impact crater.
Possible values are 1 (almost certain, 80 to 100% confidence),
2 (probable, 30% to 80% confidence), and 3 (cannot be ruled out
as an impact structure, <30% confidence). Confidence levels
are subjective, but are generally based on the presence or
absence of such features as "hummocky" ejecta, well-defined
ejecta deposits, rough walls, terracing (larger craters only),
and a central peak or peak ring (larger craters only).
Volcanic structures, the features most often confused with
impact craters, usually are steep-sided, have smooth inner
walls, and have smaller, less complete (if any) ejecta deposits
than impact craters.
Elevation (Ev) of surrounding terrain. Made by taking 4-point
average of global topography data (5 km/pixel sampling) located
3 diameters away from the crater center.
Crater density at a crater's location (Rho). Value is the
density of craters in the neighborhood of the specified crater.
This is calculated by counting the number of craters (including
the specified crater) within a 1000 km radius circle, and
normalizing to give the number of craters per 1 x 106 km2.
Twenty-five pixel averages of the DN values (an 8 bit, unsigned
integer for each pixel in the SAR image) of a representative
location on the crater floor (dni) and a location in the
terrain surrounding the crater (dno). A representative
location in the crater floor is similar in brightness to the
majority of the crater floor. A representative location in the
terrain surrounding the crater is a piece of terrain near the
crater that is similar in character to the terrain that the
crater formed on but that is unaffected by the crater. Within
the crater we chose a piece of floor that appeared to be
similar in brightness to the majority of the floor material.
The difference between these values (dnd) gives an estimate of
the relative radar brightness of the crater interior.
Individual DN values can be converted to radar cross section in
decibels by the formula
The average DN is the average of the logarithm of the
backscatter at each pixel location. This calculation was only
made for craters > 16 km in diameter.
Maximum distance of radar-bright continuous ejecta (Ce) from the
rim. This does not include ejecta that was obviously emplaced
as long run-out flows. Error is ± 0.9 km.
Maximum distance from rim of all flow units (Fl) extending from
the ejecta blanket. Error is ± 0.3 km.
Approximate diameter of dark halo (Dh) surrounding crater. Error
is ± 5%.
Completeness of ejecta deposits (Ec) around the rim as a fraction
of 1. Error is ± 0.05.
Completeness of the rim (Rc) as a fraction of 1. Error is ±
0.05.
Planform of the crater rim (Pl): (c)ircular, (e)longate,
(i)rregular, and (p)olygonal
Morphologic class (Mo) : (1) bowl-shaped; (2) knobby base; (3)
central peak; (4) multiple peaks; (5) peak rings; (6) multiple
rings; and (0) indistinguishable flat-floored feature, albedo
line, etc.
Central structure diameter (Cd). Value is actually diameter of a
circle with an area equivalent to that encompassing any central
structure; measured in the same manner as rim-to-rim diameter.
Previous studies have measured peak ring diameter by fitting a
circle to the peaks of the ring massif (e.g., Pike and Spudis
1987, EM &P, v. 39, 129). For the sake of interplanetary
comparisons in the text we also used this older technique to
measure peak ring diameters for single- and double-ring basins.
Peak ring diameters using this second technique are in the
separate sheet. Error for central peak or peak ring diameter
using the equivalent area technique is ± 6%. Error for peak
ring diameter using the circle-fitting technique is ± 1.7 km.
Wall (Wa) terracing. Denotes whether the wall appears
(u)nterraced or (t)erraced at C1-MIDR resolution.
Wall width (Ww) (Fig. 10). To minimize distortion resulting from
SAR effects, horizontal distance from rim to floor was measured
in the N - S direction. If no clear break between wall and
floor could be discerned, this measurement was not made. Error
is ± 10%.
Multiples (Mu). Impact event is classified as either a (s)ingle
crater, one with (m)ultiple floors and a single rim, or a
(f)ield of craters.
Floor reflectivity (Fr). In qualitative terms, does the floor
appear (b)right, (i)ntermediate or (d)ark.
Parabolic feature (Pf) associated with crater -- yes, no, maybe.
We used only definitely parabolic features in SAR images that
could not be attributed to processes other than crater
formation.
Apparent projectile direction of travel (Pd). A qualitative
assessment based on crater shape and orientation of ejecta
deposits.
Multiple asteroid (Ma). A few impact craters are unusually close
together, but too large and too far apart to be from a single
impactor. These are assumed to be the result of binary (or
more) asteroids (or comets) striking simultaneously. The
individual craters of these events are listed separately, but
are linked by an identical number in this column.
Terrain type that crater lies on: undistinguished plains (p),
fractured plains (pf), Lakshmi planum (lp), tessera and
mountain belts (t), corona (c), volcanic regions (v), ridge
belt (r), and rift (ri).
Interior flat floor (If) -- yes, no, maybe. The crater floor has
an areally extensive flat surface as if emplaced by a fluid
that then cooled in situ, without obvious breaching or
overflowing of the rim by exterior processes.
Embayment and/or filling of crater or its ejecta blanket by
obviously exterior processes (Ee) -- yes, no, maybe.
Tectonic deformation (T) of crater by exterior processes -- yes,
no, maybe.
Degradation state (De) as defined in Basilevsky et al. (1987, JGR
v.92, 12,869): (1) pristine, apparently intact ejecta deposits;
(2) degraded, small amount of ejecta; and (3) highly degraded,
can barely tell it's a crater.
Entries in Multiple Impacts Database
Some entries are taken directly from the main database. See
above for descriptions of Name, Lat, Lon, Co, Mo, and Mu. The
other entries are as follows, and were only measured for
Confidence Level (Co) 1 and 2 craters:
Diameter (D). An equivalent diameter of the entire area
encompassed by the multiple-floored crater or crater field.
Measured as D is for the main database. NOTE: For crater
fields, the equivalent single crater diameter (SD) is used for
D in the main database.
Properties (Pr). Properties of the ejecta blanket and shape of
the crater(s) indicative of impact angle: (1) asymmetric ejecta
blanket (45-60 degrees), (2) missing ejecta uprange (30-45
deg.), (3) partially missing ejecta downrange (15-30 deg.), (4)
butterfly ejecta pattern (0-15 deg.), (5) steepening of crater
walls uprange (15-30 deg.), (6) elongate crater shape (0-15
deg.), (7) ricochet fragments (0-15 deg.), and (8) single
ricochet crater (0-15 deg.). Classification based primarily on
Gault and Wedekind (1978, Proc. LPSC 9, 3843).
Impact angle (Ia). Based on properties of the ejecta blanket and
crater shape, Impact angle is assessed in 15 degree increments:
(1) 0-15 deg., (2) 15-30 deg., (3) 30-45 deg., (4) 45-60 deg.,
(5) > 60 deg..
Largest crater's diameter (Ld) and other craters' diameters
(2-6).
Equivalent single crater diameter (SD). Using the diameters of
the individual craters and a simple crater scaling law,
calculates the equivalent diameter crater that would have been
produced had the incoming meteoroid not broken apart.
Maximum downrange separation (Md) of craters.
Maximum crossrange separation (Mx) of craters.
Maximum total separation (Mt) of craters.
Number of crater farthest downrange (Dr).
Number of crater farthest from the largest crater (Cf).
Diameter of crater farthest from the largest crater (Fd).
Entries in Rings Database
This database lists the measurements of ring diameters for
peak-ring craters and multi-ring basins. Ring diameters are
measured from the diameter of the best-fit circle that runs along
the rim crest of craters. As described in the main database, we
also measure the area encompassing the central structure and
calculate an equivalent diameter (Cd).